If you have a decent sized monitor, Split View in El Capitan 10.11 can be very helpful. I use it frequently when I need to work on two apps simultaneously or just switch between two frequently without Command-Tab. If you have not yet tried Split View, you are missing out.

There are two ways to fire up Split View. One is via Mission Control. If you run an app in full-View mode, you can then drag another compatible app (just about everything is) to its thumbnail at the top of the Mission Control View to open both apps in Split View. I found that way very difficult, so I do it the other way, which is to simply click on the green button window size control and hold it. Apps that will work with Split View have a different looking green button than those that are not.

The app changes to full screen, but only half of your screen is used. The rest of your screen shows other open apps; click on one to have it take up the rest of the Split View screen.

That's great, but here's what many reviews have missed: if you Command-Tab back to some other app, you can put that one into Split View mode along with a fourth app and so on. Command-Tab will then let you switch back and forth between your regular apps and all those you have open in Split View.